Beside means next to:
* A house beside the sea
* She sat beside her friend.
Besides
As a preposition, besides means in addition to or apart from
* What are you studying besides English? (in addition to)
* Who was there besides Jon? (apart from)
As an adverb, besides means as well or furthermore.
* He was scruffy and badly prepared. Besides, he turned up late for the interview.
